The recent observation of the sustained level of acetylcholinesterase (AChE) in incubated homogenates of normal superior cervical ganglia (SCG) of the cat and rat, in comparison with its more rapid fall in those in which butyryl- or propionylcholinesterase (BuChE or PrChE) had been alkylphosphorylated selectively by treatment with iso-OMPA in vivo, is consistent with the proposal that BuChE and PrChE serve as post-transcriptional precursors of AChE. The mechanism of this phenomenon will be studied. Butyrylcholinesterase has been demonstrated in high concentrations at the dendritic membranes of all ganglion cells of the cat SCG; however, this enzyme is absent from the granular endoplasmic reticulum. Its source at the former site is being investigated. We shall continue the search for the neurotrophic factor responsible for the maintenance of AChE at post-junctional dendritic membranes, from which it disappears within a few days following denervation.